也许最困难和最有趣的步骤是开发一个特定的，可测试的假设。一个有用的假设通过应用演绎推理来实现预测，通常以数学分析的形式。这是关于特定情况下的因果关系的有限陈述，可以通过实验和观察或通过对所获得数据的概率的统计分析来测试。测试假设的结果目前尚不清楚，因此结果可以提供有关假设有效性的有用数据。当已知假设对其有效性有限时，模型用于这种情况。例如，原子的玻尔模型描绘的电子以类似于太阳系中的行星的方式环绕原子核。该模型可用于确定简单氢原子中电子量子态的能量，但它绝不代表原子的真实性质。科学家（和理科学生）经常使用这种理想化的模型来初步掌握分析复杂情况的方法。科学理论或法律代表了一种假设（或一组相关的假设），这种假设通过反复测试得到证实，几乎总是在多年的时间里进行。一般来说，理论是对一系列相关现象的解释，如进化论或大爆炸理论。一旦建立了科学理论，就很难让科学界抛弃它。在物理学中，以太作为光波传播媒介的概念在19世纪后期遭到了严重的反对，但直到20世纪初，当阿尔伯特·爱因斯坦提出对不依赖于光的波浪性质的替代解释时，它才被忽视。传播媒介。如今，物理学家很少将“法律”这个词应用于他们的想法。在某种程度上，这是因为之前发现的许多“自然法则”并不像指导方针那样多，而是在某些参数范围内有效，但在其他参数范围内则不然。有时会产生一种必须等待新知识或技术可测试的假设。原子的概念是由古希腊人提出的，他们无法对其进行测试。几个世纪之后，当有更多知识可用时，该假设得到了支持并最终被科学界所接受，尽管它在一年中不得不多次修改。正如希腊人所认为的那样，原子并不是不可分割的。 “法律”一词通常是指一个与理论中不同要素相关的特定数学方程式。帕斯卡定律是指描述基于高度的压力差异的等式。在艾萨克·牛顿爵士发展的万有引力的整体理论中，描述两个物体之间引力的关键方程称为引力定律。科学哲学家托马斯库恩（Thomas Kuhn）发明了科学范式一词来解释科学运作的理论工作集。他对一种范式被推翻以支持一套新理论时所发生的科学革命做了大量工作。他的研究表明，当这些范式明显不同时，科学的本质就会发生变化。相对论和量子力学之前物理学的本质与发现之后的本质不同，正如达尔文进化论之前的生物学与其后的生物学根本不同。调查的性质发生了变化。科学方法的一个后果是试图在这些革命发生时保持调查的一致性，并避免企图在意识形态的基础上推翻现有的范式。
Perhaps the most difficult and intriguing step is the development of a specific, testable hypothesis. A useful hypothesis enables predictions by applying deductive reasoning, often in the form of mathematical analysis. It is a limited statement regarding the cause and effect in a specific situation, which can be tested by experimentation and observation or by statistical analysis of the probabilities from the data obtained. The outcome of the test hypothesis should be currently unknown, so that the results can provide useful data regarding the validity of the hypothesis. A model is used for situations when it is known that the hypothesis has a limitation on its validity. The Bohr model of the atom, for example, depicts electrons circling the atomic nucleus in a fashion similar to planets in the solar system. This model is useful in determining the energies of the quantum states of the electron in the simple hydrogen atom, but it is by no means represents the true nature of the atom. Scientists (and science students) often use such idealized models to get an initial grasp on analyzing complex situations. A scientific theory or law represents a hypothesis (or group of related hypotheses) which has been confirmed through repeated testing, almost always conducted over a span of many years. Generally, a theory is an explanation for a set of related phenomena, like the theory of evolution or the big bang theory. Once a scientific theory is established, it is very hard to get the scientific community to discard it. In physics, the concept of ether as a medium for light wave transmission ran into serious opposition in the late 1800s, but it was not disregarded until the early 1900s, when Albert Einstein proposed alternate explanations for the wave nature of light that did not rely upon a medium for transmission. These days, physicists rarely apply the word “law” to their ideas. In part, this is because so many of the previous “laws of nature” were found to be not so much laws as guidelines, that work well within certain parameters but not within others. Sometimes a hypothesis is developed that must wait for new knowledge or technology to be testable. The concept of atoms was proposed by the ancient Greeks, who had no means of testing it. Centuries later, when more knowledge became available, the hypothesis gained support and was eventually accepted by the scientific community, though it has had to be amended many times over the year. Atoms are not indivisible, as the Greeks supposed. The word “law” is often invoked in reference to a specific mathematical equation that relates the different elements within a theory. Pascal’s Law refers an equation that describes differences in pressure based on height. In the overall theory of universal gravitation developed by Sir Isaac Newton, the key equation that describes the gravitational attraction between two objects is called the law of gravity. The science philosopher Thomas Kuhn developed the term scientific paradigm to explain the working set of theories under which science operates. He did extensive work on the scientific revolutions that take place when one paradigm is overturned in favor of a new set of theories. His work suggests that the very nature of science changes when these paradigms are significantly different. The nature of physics prior to relativity and quantum mechanics is fundamentally different from that after their discovery, just as biology prior to Darwin’s Theory of Evolution is fundamentally different from the biology that followed it. The very nature of the inquiry changes.One consequence of the scientific method is to try to maintain consistency in the inquiry when these revolutions occur and to avoid attempts to overthrow existing paradigms on ideological grounds.